Retarding circuit



March 3, 1959 c. D. RUSH ETAL 2,876,396

RETARDING CIRCUIT Filed March 16, 1955 TO R O y sUZEAEENRY /g j 53 H 11 H 12 H WATER WATER I WATER I FLOW I :l FLOW I FLOW I l DETECTOR DETECTOR DETECTOR i 7 7 L n H A United RETARDHNG CIRCUIT Charles D. Rush, Valley Stream, N. Y., and Manfred W. Muehter, Nutley, N. J., assignors to American District Telegraph Company, Jersey City, N 3., a corpo' ration of New Jersey Application March 16, 1955, Serial No. 494,777

3 Claims. (Ci. 317-441) This invention relates to protection circuits and more particularly to such circuits by which a central alarm device is linked with and may be actuated from any one of a plurality of remote points along the circuit thereby to indicate a variation in a local condition.

Such installations are often utilized for the purpose of signalling and giving an alarm on the occurrence of a hazardous condition as in the case of a fire. For example, waterflow detectors are installed in automatic sprinkler systems which, on the occurrence of a flow of water due to a fire, actuate a transmitting device which in turn transmits a signal over the signal network to the central station.

It is desirable and often important that the detection apparatus be capable of discriminating between the hazardous condition which is to be guarded against and occurrences which, though capable of actuating the apparatus, are not representative of a hazardous condition. Thus, in the case of automatic sprinkler installations false alarms are often initiated due to internal pressure variations which cause a surge or flow of water. Although such conditions are transient in nature and are of relatively short duration they, nevertheless, may actuate the detector. It has heretofore been proposed to utilize delaying or retarding mechanisms of one type or another adjusted so as to prevent the initiation of an alarm unless the condition continues for at least a predetermined length of time. Such retarding mechanisms have heretofore been provided in various forms including hydraulic, pneumatic or electric devices. The electric retarding devices heretofore proposed for use in connection with detecting and alarm transmitting systems have been unsatisfactory for various reasons. The transient conditions which might otherwise occasion the initiation of a false alarm may occur at random and often at relatively short intervals. On the other hand, the recycling time of the apparatus was of such long duration as to span two or more occurrences of the transient condition. Consequently, even though any one occurrence may have been of too short duration to actuate the detecting apparatus, failure of the retarding device to recycle completely in the interval resulted in the successive occurrences being cumulative and thereby serving to initiate a false alarm.

Another disadvantage of electrical retarding devices heretofore proposed for use in such installation resided in the necessity for installing additional power wiring from the power supply to such points where it was desired to introduce a period of retardation. in addition to entailing an excessive installation cost, such an arrangement is also costly to maintain.

It is, therefore, a principal object of this invention to provide an improved signaling network for initiating the transmission of a signal on the occurrence of a change in a local condition.

Another object is to provide such a network which substantially reduces the occurrence of unnecessary signals or false alarms and which may be installed and maintained at a relatively low cost.

A further object is to provide a highly simplified net- 2,876,396 i-atezated Mar. 3, 1959 M work for use at a local installation for initiating the transmission of an alarm signal to a central supervisory station and having a plurality of remote contacts actuation of which on the occurrence of a change in a local condition may be individually regulated to provide enhanced freedom from unnecessary signals.

A more specific object is the provision of a retarding circuit for controlling the flow of current when normally open contacts of a signaling network are closed which is highly efiicient though relatively simple and which is energized by the central power supply of the network.

In accordance with this invention there is provided a network having two loop circuits each connected to opposite sides of the normally open contacts of one or more detector units responsive to a variable condition whereby upon the occurrence of a change in the condition the contacts are closed to cause the operation of a signaling device. In order to render the network insensitive to transient short duration condition changes the contacts are shunted by a capacitor which is charged by the network line voltage and which, on closing of the associated shunted contacts, discharges through the coil of a relay to thereby open relay contacts in series with the associated shunted contact. Means may also be provided to permit adjustment of the duration of the discharge time of the capacitor as well as means to provide charging current of predetermined polarity to the capacitor. A variable resistor in parallel with the relay winding may be utilized to control the capacitors discharge cycle, while a rectifier bridge between the capacitor and the network avoids the possibility that the polarity of the voltage across the capacitor may be reversed.

Further objects and advantages of this invention will be apparent from the following description thereof and the accompanying drawing in which:

Figure 1 is a schematic representation of one type of installation in accordance with this invention; and

Figure 2 is a detailed schematic representation of the retarding circuit means.

The present invention is especially well suited for use in a network it! installed in a subscribers premises and associated with an automatic water sprinkling system. The network includes two loop circuits A and B connected to opposite sides of normally open contacts 11-13 each of which is governed by water flow detectors indicated schematically at 1416 respectively. There are various types of waterflow detectors commercially available which are constructed or may be readily adapted to actuate contacts 11-43. The specific construction of the waterfiow detector forms no part of the present invention and is therefore not shown in detail in the drawings. The water sprinkling system may include several risers or conduits 17-19 each of which connects a water main 20 to a set of sprinkler heads. A waterflow detector is shown as installed in each of the risers 1719 and closes its associated contacts when a flow of water occurs in the riser.

Network loops A and B are connected in series through an alarm relay RA and also through an impedance element, shown as a winding R1, so that a limited amount of power flows through loops A and B from power supply unit 21 to which they are also connected. The circuit constants are so chosen that relay RA is deenergized under these conditions; the resistance of winding R1 being such that when it is shunted out on the closing of any of the normally open contacts 11-43 the current flowing in the circuit increases to a value sufficient to energize alarm relay RA. Operation of the alarm relay RA may initiate the ringing of a hell or operation of an annunciator. As indicated, relay RA and winding R1 may be part of a transmitter unit 22 provided for transmitting an alarm signal over a supervisory network 23 to a supervisory station upon initiation of a sequence of events due to actuation of alarm relay RA. Various types of such transmitting units are well known and consequently it is not necessary to describe transmitter unit 22 in detail here.

It has been customary to provide a retard mechanism of one type or another which introduces a delay period between energization of relay RA and initiation of an alarm signal. Such an arrangement is utilized to avoid the transmission of false alarms which may be occasioned by short duration transient conditions in the water system. Simply stated, in the event of a sudden pressure change in the water system a water current surge may take place which momentarily actuates the waterfiow detectors and leads to the closing of one or more of the contacts in network 1.0. It will readily be understood that when any one of the waterfiow detectors is actuated for a period which is less than that of the retard period of the delay mechanism relay RA will in effect become deenergized before expiration of the delay period, the

delay mechanism thereby preventing initiation of an alarm. As thus far described, network It) is representative of a class of protection loop circuits heretofore in use.

Such circuits having centrally located retard mechanisms which affect the operation of the entire system may be satisfactory in relatively simple installations. In other installations such an arrangement has proven unsatisfactory for various reasons, one of which being that the system as a whole is unnecessarily and objectionally desensitized in order to avoid the transmission of a false alarm. Assume, for purposes of illustration, that a water current surge occurs in the water main having a duration of 6 seconds at a given point and traveling at such velocity that 3 seconds are required for the surge to travel along the water main from riser 17 to riser 18 and from riser 18 to riser 19. It is apparent then that contacts 1113 will each be actuated in succession at 3 second intervals and each will be closed by its waterfiow detector for 6 seconds. In order to prevent transmission of a false alarm in this instance a retard period of more than 12 seconds is required to effectively deal with a 6 second surge when a central retard mechanism is utilized.

Another disadvantage of protection circuits which incorporate a central retard mechanism is occasioned by the fact that in many installations the detection devices which may be associated with such contacts as contacts 11 to 13 are exposed to quite different conditions. For example, waterfiow detector 14 and contacts 11 may be so situated that a retard period of two seconds may provide adequate protection against false alarms. On the other hand waterfiow detector 16 and contacts 13 may require a retard period of approximately seconds. To avoid the occurrence of false alarms, systems utilizing a central retard mechanism must be operated with a minimum retard period of ten seconds thereby imposing the longest retard period required by any one of the detection devices upon the entire system.

Referring now to Figure 2, a retard circuit 24 is associated with each of the contacts 11, 12 and 13 although illustrated in detail only in connection with contacts 11. Contacts 11 are connected between protection loops A and B in series with normally closed contacts RT; of retard relay RT. Capacitor 25 is connected in shunt with contacts 11 and in series with the winding of retard relay RT. Rectifier 26 is connected in series with capacitor 25 and power supply 21 and in shunt with the winding of relay RT so that when current is flowing to charge capacitor 25 relay RT is by-passed. A variable resistor 27 is also connected in series with capacitor 25 and in parallel with relay RT thereby providing a convenient means for adjusting or varying the retard period of the circuit.

Power supply unit 21 is connected to the usual line power supply as indicated in Figure 1 and is adapted to 4 convert the available electric power to a form which is suitable for the operation of network 10. As is conventional with such power supply units, it may also supply power temporarily in the event of line power interruption. In order to avoid the possibility that the polarity of the potential applied across capacitor 25 may be reversed, a rectifier bridge 28 is connected between protection loops A and B in series with contacts RT Conductor 29 connects the positive side of rectifier bridge 28 to one side of normally open contacts 11 and to capacitor 25, while conductor 36 connects the negative side of the bridge to the common junction of contacts 11, rectifier 26 and on one side of the winding of retard relay RT.

With contacts 11 open and contacts RT closed, capacitor 25 is charged due to the flow of current from rectifier bridge 28 along conductor 29 and along conductor 30 to the other side of rectifier bridge 28, the charging current by-passing relay RT through rectifier 26. When, due to the operation of waterfiow detector 14, contacts 11 are closed, capacitor 25 discharges through closed contacts 11 and the winding of relay RT; rectifier 26 presenting a high impedance to the discharge current. While capacitor 25 is discharging relay RT is energized thereby opening normally closed contacts RT Consequently, even though contacts 11 have closed, winding R1 (Figure l) is not by-passed and alarm relay RA remains deenergized. The time duration of the discharge from capacitor 25 and hence the length of the retard period depends upon the circuit constants of the components utilized. Furthermore, by adjustment of variable resistor 27 the duration of the discharge of capacitor 25 may be varied as desired. Assuming that the condition which resulted in the actuation of waterfiow detector 14 and the closing of contacts 11 continues uninterrupted capacitor 25 will become discharged. Relay RT is once again deenergized and contacts RT return to their normally closed position. Now winding R1 is shunted due to the connection of loops A and B through contacts 11 and RT; and the increased current which flows through alarm relay RA is sufficient to energize the same and an alarm signal is initiated.

Turning now to a consideration of the operation of the circuit when contacts 11 became closed due to a short duration variation in the condition to which the detection device associated with the contacts is responsive, capacitor 25 will begin discharging through relay RT as soon as contacts 11 are closed to cause the opening of contacts RT While capacitor 25 is still discharging contacts 11 open thereby stopping further discharge of the capacitor and deenergizing relay RT which is in turn followed by the closing of contacts RT Also upon the opening of contacts 11 capacitor 25 is very rapidly recharged. This follows from the fact that a relatively low impedance path is provided for the charging currents through rectifier 26 and rectifier bridge 28. In fact, the recharge time of capacitor 25 may be about A of a second or less even though its discharge time may be about 15 seconds or more depending upon the circuit con stants of the components utilized. The charge-up time of about 1 of a second is representative of the recycling time of the retard circuit and, since it is relatively short, effectively prevents or minimizes the possibility that successive operations of the detection device for short periods at closely spaced intervals may have a cumulative elfect and serve to cause the initiation of an alarm signal even though any one of the operations was of a duration less than the retard period.

A further advantage resides in the fact that for practical purposes there is no additional current drain due to the presence of retard circuit 24 once capacitor 25 is charged. Current leakage across capacitor 25 and the rectifier is very small and may be ignored.

It will be observed that retard circuit 24 may be provided at each of the locations along network 10 where there is a detection device such as waterfiow detectors 14 to 16 and the contacts associated therewith. The detection device is usually located at some considerable distance from the power supply unit. The fact that additional power wiring to the retard circuits is not required is an important advantage of the present arrangement.

The terms and expressions which we have employed are used as terms of description and not of limitation, and we have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. In a flow signaling system, at least one flow detection device having normally open contacts which are closed upon the occurrence of a fluid flow to which the detection device is responsive, first and second loop circuits connected across a power supply and coupled through an impedance element in series with the power supply, said impedance element maintaining the normal current through said loop circuits below a predetermined value, signal actuating means responsive to an increase in the current in said loop circuits above said predetermined value for initiating an alarm signal, a rectifier bridge circuit having two pairs of opposite terminals with one pair of opposite terminals connected between said first and second loop circuits and the other pair of opposite terminals connected to opposite sides of said normally open contacts, said normally open contacts being in shunt with said impedance element, retard means for arresting for a predetermined time interval the efiect of actuation of said detection device to close said normally open contacts thereby to shunt said impedance element, said retard means comprising a capacitor connected in shunt with said normally open contacts and in series between said other pair of opposite terminals so as to be normally maintained charged, a relay connected in series between said capacitor and one side of said normally open contacts, normally closed contacts governed by said relay and connected in series between one of said loop circuits and the rectifier bridge circuit terminal connected thereto, a rectifier connected between said capacitor and said one side of said normally open contacts and in shunt with said relay, whereby said capacitor discharges through said relay thereby energizing said relay to open said normally closed contacts for a predetermined interval when said normally open contacts are closed so that said impedance means is maintained in series circuit with said loop circuits and said signal actuating means is held unenergized for said interval, and means for varying the duration of the current flow through said relay and including a variable impedance in shunt with said relay.

2. The flow signaling system as set forth in claim 1 wherein means are provided for connecting said signal actuating means across the power supply to which said first and second loop circuits are connected.

3. The flow signaling system as set forth in claim 1 wherein conductive means are provided for connecting said signal actuating means across the power supply to which said first and second loop circuits are connected, said conductive means serving also to complete the connection between said first and second loop circuits and the power supply.

References Cited in the file of this patent UNITED STATES PATENTS 2,078,043 Turner Apr. 20, 1937 2,249,488 Nickle July 15, 1941 2,427,750 Snyder Sept. 23, 1947 2,635,197 Routledge Apr. 14, 1953 FOREIGN PATENTS 481,054 Great Britain Mar. 4, 1938 

